The invention relates to a plastic cleaning brush, particularly a toothbrush, having a handle and an elongated brush head, which comprises a bristle carrier tapering in longitudinal cross-section from the handle to the front end of the brush head and bristles fixed thereto, where on exceeding a given pressure of the bristles on the surface to be cleaned, the bristle carrier can be deflected in an elastically flexible manner.
Conventional toothbrushes, whose handle and brush head and optionally a tapering neck interposed between them are injection molded in one piece from plastic and whose brush head is covered with bristle bundles, as a function of the dimensioning of the cross-sections and the choice of the plastics material have a certain elasticity, which cannot meet the special requirements in connection with tooth and mouth care. These special requirements are constituted by the differing outer contour of teeth with convex outer faces and concave inner faces to which it is not possible for a rigid brush head to adapt. In addition, discontinuities exist in the tooth contours due to the interdental spaces and the latter are only reached by the bristles if on the one hand the bristles have an adequate elasticity in order to evade on the free tooth faces and on the other the pressure of the brush head is sufficiently high. In addition, the toothbrush and in particular its bristles must be so designed that no local pressure peaks occur, which could lead to injuries on the dental enamel and in particular on the gingiva.
The need for a design adaptation of the toothbrush to these special features have been recognized by the experts. These documents are referred to in the following discussion of the prior art with the reference numerals used in the list.
The toothbrush described in (1) comprises a substantially flexurally stiff handle and a brush head fixed thereto and whose longitudinal cross-section tapers in wedge-shaped manner towards the front end in order to also be able to reach narrow areas of the oral cavity without an excessive bending aside of the bristles. The brush head is made from rubber or some other resilient material and a flexible, steel stiffening rod embedded therein and tapering towards the end of the brush head. The bending behavior of the brush head is exclusively determined by the rod-like insert, because the surrounding rubber sleeve has no significant bending resistance. The insert in conjunction with the pressure applied to the handle determines the pressing action on the teeth to be cleaned or the gums to be massaged. As a result of the tapering of the steel insert there is a spring constant which decreases from the handle to the front end of the brush head and, for a given pressure, a deflection of the bristle carrier receiving the bristles which progressively increases towards the front end of the brush head. As a result of the rod-like construction of the insert this deflection also occurs transversely to the brush longitudinal axis, so that the brush head cannot be guided in a controlled manner. The brush head is connected to the handle by a metal sleeve. Due to this and due to the steel insert there is a costly manufacturing procedure. Moreover, due to the metal parts, the toothbrush does not comply with modern requirements.
Another known construction (2) has a substantially rigid handle, to which is connected by an adhesive joint a brush head made from flexible material, e.g. rubber. The brush head also tapers from the handle to the front end and is curved in concave manner towards the bristles. This is intended to cover the outer contours of the denture in the front tooth area, whereas in the back tooth area the brush head gives way due to its rubber elasticity. Adaptation also results through a deflection to a convex curvature on the bristle side of the inner contour of the teeth. These characteristics cannot or cannot adequately be implemented with a one-piece molding forming the brush head.
In the toothbrush described in (3) the brush head is in two parts. The handle-near area of the bristle carrier is manufactured in one piece with the handle and is not bendable. To the top of the bristle carrier is bonded a rubber elastic portion forming the front part of the brush head and can bend at the leading edge of the rear part of the brush head. This only permits a very incomplete adaptation to the denture contour and also the fatigue strength of the toothbrush is completely inadequate due to the critical compressive and shear forces at the transition between the two brush head parts.
According to numerous other proposals in (4) through (12), the brush head is subdivided into several segments, which are interconnected in integrally joined manner by means of plastic bridges, spring inserts or in mechanical manner, the bristle bundles being fixed to the individual segments. It has been attempted to close the gaps between the segments in certain of these known toothbrushes either by a corresponding shaping of the segments or by filling with a different plastics component. These constructions are extremely complicated from the manufacturing standpoint and have a limited fatigue strength. In addition, gaps and depressions are accepted in these known constructions or such depressions and hard edges cannot be avoided for manufacturing reasons. Thus, they neither meet the use requirements, nor the hygienic requirements.
The same applies regarding the proposals known from (13) to (16), in which either the entire brush head is hinged to the handle or the bristle arrangement is subdivided into individual segments and even individual bristle bundles, which are mounted in a hinged manner on the brush body.
The problem of the invention is to provide a toothbrush of the above mentioned kind which are known from (2), which is constructed in such a way that the brush head is adapted in optimum manner particularly to the problem areas of the denture, namely the inner contour thereof with varying radius of curvature.
According to a first embodiment, this problem is solved in that the bristle carrier comprises two, longitudinally successively arranged portions interconnected without transition and made from materials having different characteristics and at least the front portion is formed from an elastomer and that the materials, cross-sections and bending length of the portions are chosen in such a way that the front portion is deflectable with a smaller radius of curvature than the other portion.
As a result of the inventive construction, it is firstly possible to avoid any segmentation of the brush bead, as well as any hinged connections between the brush head parts. The brush head forms a single entity, but has a differentiated bending behavior over its length, in that the elastomer, front portion in the case of a smaller contact pressure and/or a greater curvature of the denture contour gives way more strongly than the other portion of the brush head, whose deflection occurs with a stronger contact pressure and/or a reduced curvature of the denture contour, so that all the tooth faces, also on the inner contour of the teeth, are reached by the bristles with an approximately uniform pressing action.
The two portions of the brush head can be integrally joined, e.g. by welding, two-component injection molding, etc. Preferably, both portions are made from an elastomer with different rubber elasticity.
Another solution of the problem of one invention, which can optionally be combined with the first mentioned solution, consists of the bristle carrier comprising at least two portions passing, without transition, into one another, whereof the handle-near portion tapers at a wedge angle xcex2 to the transitionless connected front portion which itself tapers at a wedge angle xcex1 to the end of the brush head, in which xcex1 less than xcex2.
As a result of the differing wedge angles of the two portions of the bristle carrier, there are correspondingly differing cross-sections or moments of inertia, which lead to a differing degrees of deflection of the two portions, but to a continuous deflection within each portion.
The last-mentioned embodiment can be optimized in that the bristle carrier tapers from the handle-near area to the end of the brush head, accompanied by a continuously decreasing wedge angle. Thus, the back forms a surface continuously curved from the handle-near area with a relatively large cross-section to the front end and with a minimum bristle carrier cross-section at the front end.
To ensure a completely satisfactory guidance of the brush head, the handle-near portion is connected to the handle via a comparatively less resilient, short portion.
If between the handle and the brush head, as is frequently the case in toothbrushes, there is an elastically resilient neck reduced in cross-section compared with said two parts, said neck passes with a continuously increasing cross-section of lower bending elasticity into the handle-near brush head portion.
As a result of the bending elastic neck the entire brush head can be deflected with respect to the handle, e.g. in order to be able to avoid excessive pressure in substantially planar contours of the denture. Due to the larger cross-section in the transition area between neck and elastic brush head portion, a transverse elasticity is avoided in this area, which would make the brush head guidance more difficult.
The brush head can be positively and interchangeably fixed to the handle, but can also obviously be positively connected thereto. The interchangeable fixing offers the advantage that the brush head can be replaced in the case of bristle wear, which is desirable at relatively short intervals for hygienic and dental reasons.
If the front portion is made from elastomer, it is also advantageous for it to embrace the handle-near portion with narrow strips forming the narrow sides of the brush head, so that an elastic layer, which serves as a mucosa protection, is also obtained in this harder area of the brush head.
In a further embodiment the elastomer of the front portion extends as a layer at least under the handle-near portion or optionally up to the underside of the neck. Thus, all surfaces of the toothbrush coming into contact with the gingiva during use are rubber-elastic.
This embodiment further enables to fix all bristles of the brush head in the elastomeric parts of the brush head for example by welding, melting in or molding in. All bristles or bundles can be fixed in one single processing step and are secured under the same conditions so that the draw-off strength is the same with each bristle or bundle. As the bristles or bundles respectively are fixed with their ends in the flexible elastomer, these ends can reciprocate to a certain degree so that the contact pressure is additionally controlled.
According to another embodiment the bristle carrier can be concave curved in continuous or discontinued manner to the bristles, so that in the pressureless starting position an adaptation to the convex outer contour of the denture is possible.
The envelope enclosing the ends of the bristles can essentially be a plane, it being possible for the bristle ends within a bundle or individual bundles or groups of bundles to project or be set back with respect to said envelope, in order to obtain an optimum action on the tooth surface and in the inter-dental spaces.
Instead of this the envelope enclosing the ends of the bristles can be continuously or discontinuously concavely curved to the bristles and preferably the bristles or bundles have in the front portion of the brush head a length increasing towards its end. This also permits an optimum adaptation to the outer contour of the denture.
The invention is described in greater detail hereinafter relative to embodiments and the attached drawings, wherein show: